GHRP-6
Growth Hormone Releasing Peptide-6, Growth hormone-releasing hexapeptide, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2
Mechanism of action of Hexarelin. I. Growth hormone-releasing activity in the rat.
Torsello. A A; Grilli. R R; Luoni. M M; Guidi. M M; Ghigo. M C MC; Wehrenberg. W B WB; Deghenghi. R R; Müller. E E EE; Locatelli. V V
Key Findings
- Repeated Hexarelin dosing (80 µg/kg twice daily) boosts the GH response to a later dose in 10‑day‑old rat pups.
- The same priming effect does not occur in adult male rats, even after 5 days of dosing.
- Hexarelin’s GH‑releasing action involves multiple pathways: a minor direct pituitary effect, an indirect effect via GHRH, and a likely unknown hypothalamic factor.
Practical Outcomes
- For biohackers, the data suggest that short‑term, repeated GHRP‑6 dosing may not increase GH responsiveness in adults, so “loading” the peptide likely won’t amplify later doses. The peptide’s effect appears to rely partly on the body’s own GHRH system, meaning that combining GHRP‑6 with strategies that support GHRH (e.g., adequate sleep, low stress) could be more effective. No new dosing protocol is recommended beyond what is already common.
Summary
Hexarelin, a synthetic version of GHRP‑6, can trigger growth‑hormone release in rats. In young rats, giving it for several days makes the body respond more strongly to a later dose, but this “priming” effect isn’t seen in adult rats. The peptide seems to work in three ways: a small direct hit on the pituitary, by causing the brain to release the natural hormone‑releasing factor GHRH, and possibly by an unknown brain signal that works together with GHRH.
Abstract
We have reported Hexarelin (HEXA), an analog of growth hormone-releasing peptide 6 (GHRP-6), potently stimulates growth hormone (GH) secretion in infant and adult rats. This study was undertaken to further investigate Hexarelin's mechanisms of action. In 10-day-old pups, treatments with HEXA (80 micrograms/kg, b.i.d.) for 3-10 days significantly enhanced, in a time-related fashion, the GH response to an acute HEXA challenge. Qualitatively similar effects were elicited in pups passively immunized against growth hormone-releasing hormone (GHRH) from birth. In adult male rats, a 5-day pretreatment with HEXA (150 micrograms/kg, b.i.d.) did not enhance the effect of the acute challenge, and the same pattern was present after a 5-day pretreatment in male rats with surgical ablation of the mediobasal hypothalamus (MBH-ablated rats). In addition, in adult sham-operated rats, Hexarelin (300 micrograms/kg, i.v.) induced a GH response greater (p < 0.05) than that induced by GHRH (2 micrograms/kg, i.v.). However, in MBH-ablated rats 7 days after surgery, GHRH was significantly (p < 0.05) more effective than HEXA, and 30 days after surgery HEXA and GHRH evoked similar rises of plasma GH. Finally, the in vitro Hexarelin (10(-6) mol/l) effect was transient while GHRH (10(-8) mol/l) induced a longer lasting and greater GH release. Three different mechanisms, not mutually exclusive, are postulated for Hexarelin stimulation of GH secretion in vivo: a direct action on the pituitary, though of minor relevance; an indirect action that involves release of GHRH, of relevance only in adult rats; and an action through the release of a still unknown hypothalamic "factor", which in infant and adult rats elicits GH release acting sinergistically with GHRH.
Study Information
pubmed
1996
10.1530/eje.0.1350481